In the simplest terms, having less data (tags/forms) being handled will be faster than having more data.
However, the amount of gain from deleting data is minor in most cases. As an example, if you had 300 tags and 50 lists, it would be unlikely that you would see a real world benefit to optimizing the number of tags and lists unless your server is already slow and/or underpowered.
Tags and lists are used on every login.
Tags are used constantly on every page when your users are accessing the site, and when you, as an admin, are editing pages and setting protections.
As an example of an extreme case, if you had 3,000 tags and 500 lists, you may run into some performance issues when editing the site simply due to the amount of time some page builders take to load those lists into the screen so you can use the dropdowns. Most screens don’t use dropdowns of lists, so they’re a lesser issue as well.
Forms are only used when you use the form shortcode, so the number of forms would no impact on performance.
If you do see slowdowns on your page editors, we can help you make some settings adjustments that limit which tags get displayed without actually deleting them, so that you’re not forced to do complex tag reorganization or deletion.
